In 2006, the International Astronomical Union (IAU) approved dwarf planets as a new classification category for "in-between sized" objects in our Solar System. Currently, there are three dwarf planets: Eris, Ceres, and Pluto (which was demoted from its previous status as a planet). In 2008, the IAU decided on the term plutoid as a name for dwarf planets like Pluto.
Dwarf planets look like planets, but they are not exactly the same. They orbit the Sun just like planets do. They also are large enough that their own gravity pulls them into the shape of a sphere, or ball-like shape. Dwarf planets are not satellites (moons of other planets). The fact that dwarf planets are unable to clear out their orbits by pulling smaller bodies into themselves or flinging them out of orbit is what distinguishes them from planets. (Image Right: The Dwarf Planets (Used with permission, Walter Myers)
